1. Field of the Invention
The present invention relates to the improved preparation of the alkyl carboxylates, notably the alkyl acetates, by reacting a gaseous mixture comprising carbon monoxide and hydrogen with the next lower homolog of the desired alkyl carboxylate. By "next lower homolog" as used herein, there is intended the corresponding carboxylate, in the alcohol moiety of which the alkyl radical contains one less carbon atom than the ultimately desired compound.
The process according to the present invention is more especially adapted for the preparation of ethyl acetate from methyl acetate.
2. Description of the Prior Art
Certain authors (compare Journal of the American Chemical Society, 100: 19, 1978, pages 6,238-6,239) have reported that it is possible, in particular, to prepare ethyl acetate by the hydrocarbonylation of methyl acetate in the simultaneous presence of ruthenium, an iodine-containing promoter and a proton donor (which is either HI, introduced at the beginning of the reaction or formed in situ from CH.sub.3 I, or a carboxylic acid).
However, the industrial-scale development of a technique of this type, the fundamental value of which cannot be disputed, is exceedingly compromised by the low activity of the catalyst system employed.
Recently, it too has been proposed (compare published French Patent Application No. 78/20,843) to carry out this reaction in the presence of a cobalt salt and iodine. However, the high pressures which are required for the catalyst system to develop an acceptable activity are such that it too is hardly possible to envisage industrial development of a process of this type.
Thus, a clear and present need exists in this art for a process for the preparation of the alkyl carboxylates from their next lower homologs, which process would make it possible to operate under low pressure, with an industrially satisfactory reaction rate, but without a consequent loss in terms of selectivity with respect to the ultimately desired ester.